Overall Component Many common diseases, including the most pervasive, are genetically complex; that is, they are the culmination of multiple genetic loci and are influenced by developmental and environmental factors. Metabolic pathways are also genetically complex, leading to individualized drug responses. Harnessing this complexity through complex trait analysis is the basis of personalized medicine. The overall goal of the Special Mouse Strains Resource (SMSR) is to provide biological resources for analysis of genetically complex traits. The resource currently maintains and distributes six recombinant inbred (RI) and two chromosome substitution (CS) strain sets from live colonies maintained in high barrier vivarium facilities and from cryopreserved embryos and sperm. The SMSR will continue to preserve and ensure the availability of specialized mouse strains and tools for complex trait analysis. The SMSR will also work closely with the complex trait community to assess and respond to resource needs, perform outreach and provide access to facilities for large-scale breeding and phenotyping.